Impact tools

ABSTRACT

Hydraulic impact tools are described which develop percussive forces for rock drilling and other repetitive high force applications. A self-excited oscillator is disclosed which includes a hammer and a valve coaxial with and actuated by the hammer for controlling the flow of pressurized hydraulic fluid. The hammer is accelerated away from an impact position to store energy in an energy storage system. The stored energy in the system is eventually returned to the hammer to drive it at increasing velocity back to its impact position. Accumulators forming part of the oscillator are closely coupled to the hammer by way of hydraulic galleries or channels and operate in concert with the hammer to provide energy storage characteristics for oscillator operation and to reduce fluctuations in the flow of hydraulic fluid and to provide for efficient operation of the oscillator.

Bouyoucos et al.

1 1 IMPACT TOOLS [75] Inventors: John V. Bouyoucos, Brighton; Roger L.Selsam, Perinton, both of NY.

[73] Assignee: Hydroacoustics lnc., Rochester,

[22] Filed: Apr. 24, 1974 {21] App]. No.: 463,625

[52] U.S. C1. 173/134; 91/235; 91/321; 91/328; 173/78; 173/80; 173/105[51] Int. C13. EZIC 3/20; F01B 23/06; B25D 9/20 [58] Field of Search91/235, 321, 328; 173/134l38 [56] References Cited UNITED STATES PATENTS2,749,886 6/1956 Densmore 91/321 3,322,210 5/1967 Arndt 173/1343,411,592 11/1968 Montabert 91/321 X 3,468,222 9/1969 Cordes ct al i.173/134 X Sept. 9, 1975 [57] ABSTRACT Hydraulic impact tools aredescribed which develop percussive forces for rock drilling and otherrepetitive high force applications. A self-excited oscillator isdisclosed which includes a hammer and a valve coaxial with and actuatedby the hammer for controlling the flow of pressurized hydraulic fluid,The hammer is ac' celerated away from an impact position to store energyin an energy storage system. The stored energy in the system iseventually returned to the hammer to drive it at increasing velocityback to its impact position. Accumulators forming part of the oscillatorare closely coupled to the hammer by way of hydraulic galleries orchannels and operate in concert with the hammer to provide energystorage characteristics for oscillator operation and to reducefluctuations in the flow of hydraulic fluid and to provide for efficientop eration of the oscillator.

11 Claims, 15 Drawing Figures PATENTEDSEP' 9mm SHEET 2 [If FIG. 5.

sum 3 mg 3 6 %mm a mm F, \H v g o 3 lllll 2 a H 0 LI 1 9 m m a H m m mmmmm E FIG.6.

FIG]

PATEN TED SEP 9 75 saw u o a PATENTED SEP 91975 SHEET 5 BF 8 A x, n xPv, TO DRIVE CAVITY(94) VNHTHROUGH pomuuz) v THROUGH GALLERY (I08) v AssEEN BY RETURN CHANNEL (I46) TIME PATENTEDSEP 9191s V TO DRIVE CAVITY(330) VNETTHROUGH PORT (356) m v As seen 52 A, BY RETURN g CHANNEL (370)f v TO secouo AAA CAVITY (332) X A PATENTEDSEP :915

sum 7 [If a JAG-l dJ w:

IMPACT TOOLS The present invention relates to impact tools andparticularly to hydraulically operated impact tools which generatepercussive energy. This invention is related to the invention describedin US. patent application Ser. No. 285,240, filed in the US. PatentOffice in the name of John V. Bouyoucos. on Aug. 3 l, 1972. and is animprovement thereon, and also to a patent application filed in the US.Patent Office in the name of John V. Bouyoucos simultaneously with thisapplication, all of which applications having a common assignee.

This invention is especially suitable for use in rock drilling, piledriving, demolition and rock ripping work, in construction, mining andthe like fields. The invention is particularly applicable for providingsmall size, high efficiency rock drills for use in mining andconstruction. The invention is also applicable to apparatus forgenerating high blow energies at high repetition rates (i.e., high powerlevels) and with high efficiency, thereby to obtain improved performancein any application where percussive energy at high power levels isneeded.

The related application, Ser. No. 285,240, describes tools forgenerating percussive forces at a load in which a hammer provides a masswhich is part of a mass spring oscillator system. The motion of the massis coupled to a valving mechanism in a hydraulic fluid-filled cavity,switching the pressure of the hydraulic fluid in that cavity abruptlybetween return and supply pressures to obtain driving forces whichaccelerate the mass with respect to the spring system. The energy of theaccelerated mass is transferred to the spring system which, when thevalve mechanism subsequently switches the pressure in the cavity toremove the accelcrating force, decelerates the mass to zero velocity andthen drives the mass with increasing acceleration in the oppositedirection towards the load. Percussive energy is generated upon impactof the mass with the load. The spring system is provided by a furtherhydraulic fluid filled cavity, the dynamic spring rate or stiffness ofwhich may be selected to tailor the motion of the ham mcr mass and theenergy transfer characteristics of the tool. The spring cavity may, forexample, be divided into a pressurized gas filled region and a hydraulicfluid filled region; the pressurized gas operating to reduce the dynamicspring rate or stiffness of the spring portion of the system towardszero so as to provide a constant force upon the hammer and to obtain arelaxation oscillation cycle. This oscillation cycle is especiallyuseful in generating high percussive forces in small tools as arefrequently desired in rock drilling.

The desirable energy storage and spring characteristics provided inaccordance with the invention of the above identified relatedapplication Ser. No. 285,240 can be obtained while at the same timeminimizing flow fluctuations and providing open flow channels and largeperipheral porting lengths for the fluid flow through the switchedcavity in a manner to improve the efficiency as well as to reduce thesize and simplify construction of impact tools also embodying thepresent invention.

It is therefore an object of the present invention to provide improvedimpact tools.

It is another object of the present invention to provide an improvedhydroacoustic oscillator.

It is a still further object of the present invention to provideimproved hydraulically operated percussive tools capable of providinghigh energy per blow even at high impact rates which may be configuredin a manner to reduce their size and weight.

It is a still further object of the present invention to provideimproved hydraulically operated percussive tools which are efficient inoperation.

It is a still further object of the present invention to provideimproved hydraulically operated percussive tools in which thefluctuations of flow of the hydraulic fluid are minimized and in whichthe efficiency of operation and performance is also improved.

Briefly described an impact tool embodying the invention includes ahousing in which a piston which provides a hammer can oscillatelongitudinally in a direction toward or away from a position where itmay im pact a load. The piston defines at least a first and a sec ondcavity in the housing. The volume of these cavities vary in oppositesenses with the movement of the piston in the same direction. The areaof the face of the piston which varies the volume of the first cavitywhen it moves is larger than the area of the moving face of the pistonwhich varies the volume of the second cavity. The first cavity has avalve mechanism associated therewith which includes a valve clementmoved by the piston which alternately opens and closes supply anddischarge ports into the first cavity for establishing alternating fluidpressures upon the piston at a frequency determined in part by the massof the piston and the pressure and compliance of the fluid presented tothe mass in the cavities. In order to provide a spring which stores theenergy developed when the piston is accelerated in response to the fluidpressure in said cavities, a third cavity is provided which is incommunication with the second cavity. The third cavity is alsoassociated with energy storage means which provides the spring portionof the system and may include an accumulator containing a region ofcompressible gas which affords a pressure release. This third cavitycommunicates not only with the second cavity, but also with the firstcavity, through the supply port, and with the supply of the pressurizedhydraulic fluid. Accordingly, the third cavity maintains substantiallyconstant pressure in the second cavity and in the first cavity when thesupply port is open, and simultaneously stores energy which is bydraulically coupled thereto from one of the first and second cavities.When the supply port to the first cavity is open the third cavity andits communicating channels provide a direct path for the circulation ofhydraulic fluid between the first and second cavities due to thedifference in areas presented by the faces of the piston presented tothe two cavities, thereby to reduce the net fluid volume displacementrequired of the third cavity and its associated accumulator. Theaccumulator ca pacity requirement is thereby reduced. The third cavitymay conveniently be mounted in a laterally displaced position from thepiston, thus enabling an impact tool design which is reduced in size.

The piston mass oscillates in a self-excited mode at a frequencydetermined by the mechanical and acoustical characteristics of thespring, mass and valve mechanism elements associated therewith. Thisself-excited oscillator is therefore a hydroacoustic oscillator.

The foregoing and other and additional objects, advantages and featuresof this invention will become more apparent from a reading of thefollowing description in connection with the accompanying drawings inwhich:

FIG. 1 is a plan view of a hydraulically operated impact tool of theabove mentioned application of John V. Bouyoucos which is filedsimultaneously with this application, the view being broken away toillustrate the internal construction of the tool;

FIG. 2 is a top end view of the tool shown in FlG. 1;

FIGS. 3A and 3B are fragmentary sectional views of the tool shown inPK]. 1, the views being taken along the lines 3A-3A and 3B3B in FIG. 1;

FIGS. 4, 5, 6 and 7 are fragmentary views ofthe tool shown in HO. 1 eachin a different position during the cycle of oscillation; the variousportions of the cycle depicted in each of the views being shown incurves im mediatcly above each view;

FIG. 8 is a fragmentary plan view illustrating another hydraulicallyoperated impact tool embodying this in vention.

FIG. 9 is a series of curves illustrating the displacement and flowcharacteristics of the tools illustrated in FIGS. 1 7, and ll.

FIG. is a series of curves illustrating the displacement and flowcharacteristics of the tool illustrated in FIG. 8; and

FIGS. ll. l2. l3 and 14 are transverse sectional views schematicallyillustrating tools in accordance with different embodiments of theinvention of the ap plication of John V. Bouyoucos and filedsimultaneously herewith.

Referring more particularly to FIGS. 1, 2 and 3A and B. there is shownan impact tool especially adapted for generating percussive forces fordrilling blast holes as in mining. construction. and quarrying work. Thetool has a housing 10 in which a piston 12 can execute oscillatorymotion along the longitudinal axis of the housing. The piston 12 servesas a hammer which impacts a shank l4. The shank 14 is part of an anvilsystem which transmits force pulses created by the impact of the lowerend of the piston 12 thereon to a load which may consist of a drillsteel and rock bit engaged with a rock interface. A chuck assembly 16holds the shank 14 for rotation by means of a hydraulic motor 18 whichis coupled by gearing 20 to the chuck 16. Hydraulic fluid for operatingthe motor 18 is supplied and discharged through supply and return lines22 and 24 (FIG. 2). Reference may be had to US. Pat. No. 3.640.35lissued Feb. 8. l972 and also to the patents cited therein for furtherinformation respecting the design of the shank l4 and chuck 16.

The above referenced patent also discusses the use of the passages suchas the bores 26 and 28 in the piston 12 and shank 14 in which a tube 30is located for the passage of cleansing fluid. suitably air or water.for flushing and cleaning the holes drilled by the tool. In order toprevent the reverse circulation of the cleansing fluid through the hole26 while allowing the shank 14 to move longitudinally and to rotate.Ucup seals 32 are located around the tube 30 in the shank [4. The upperend of the tube 30 may be flanged and sealed in the upper end cap 34 ofthe housing 10 by means of a hose coupling 36 which compresses a washer38 to seal the upper end of the tube 30.

The housing 10 is made up of a central member 40, an upper end cap 34and lower end 42 which may be assembled together by suitable bolts andscrew arrangements; only the bolts 46 in the upper end cap 34 beingshown to simplify the illustration. Internal of the central member is asleeve 48 which defines a central housing bore 50 in which the piston 12oscillates. 0" rings or other suitable seals 52 are provided between theinterfaces of the sleeve 48 and the central housing member 40 as well aselsewhere between the interfaces of the other housing members and partsto provide fluid seals. The seals between interfaces which slide orrotate with respect to each other are preferably of the U-cup type.

Attached to the central housing member 40 and lat crally offset withrespect to the axis of the housing are a supply accumulator S4 and areturn or discharge ac cumulator 56.

It will be understood that the hydraulic fluid is pressurizcd by asuitable pump having a supply and a return which may be connected byhoses or other lines to the tool in a closed loop circuit. In the eventan open loop circuit is used fluid may be discharged as to a sump.instead of going to the return side of the pump. Thus terms dischargeand return should be taken as comprehending flow to the pump return sideor otherwise to discharge.

The accumulators are shown disposed immediately above the hydraulicrotation motor 18. They may also be located in other locations asillustrated in FIGS. 8 and lll4. It is a feature of the invention tofacilitate the location of the accumulators 54 and 56 in a manner asshown in order to reduce the envelope (size) and particularly the lengthof the tool. The accumulators themselves have two sections 60 and 62which are clamped together as by bolts 66 which also clamp a flexiblediaphragm 56 therebetwcen. Holes 76 in the front wall of the section 60provide a channel for the entry of fluid into the accumulator andretainment of the diaphragm by the front wall. The diaphragm sepa ratesthe interior of the accumulator into two regions 70 and 72. The outerregion 72 may be filled with a compressible fluid (eg. a gas such asair) through a valve 74. The inner region 70 is filled with hydraulicfluid during operation of the tool which fluid enters through the arrayof holes 76 in the inner wall of the accumulator parts 60. When theaccumulators are filled with hydraulic fluid and air at operatingpressure levels, the diaphragm 68 assumes the position shown in dashedlines in the drawing. The accumulators act as energy storage means. aswill be explained more fully hereinafter.

The lower end 42 of the housing and the interior of the upper end cap 34are both vented to the atmosphere. An opening 93 in the end cap ventsthe region 92 and minimizes the compression of the air therein when thehammer 12 moves upwardly away from the impact point.

The piston 12 has an upper section 78 adjacent to which is a centersection 80 which is of a diameter larger than the upper section 78 so asto form a step 82 therebetween. The piston 12 also has a lower section84. The lower section 84 has a diameter smaller than the center section80 and defines another area which is presented by a step which. togetherwith the step 82, defines the differential area of the piston. The step90 may suitably have twice the area of the step 82. Other area ratiosmay be employed to achieve different force balance conditions. While thedifferential area is shown as provided by the steps 82 and 90, it may bepresented by other surfaces which may be made up of a plurality of stepsor may e of curved shape. such areas or surfaces nevertheless haveforces thereon the net total of which depend upon the pressure levelsand the net projected areas in a plane normal to the axis of pistonmotion, such net projected areas being referred to generally by the termfaces herein.

The lower section of the piston 12 is formed with a ring 86 and anotherring 88 which is spaced therefrom, which rings operate the valvemechanism 85 and will be described in detail hereinafter.

The end faces of center section 80 of the piston 12 define two variablevolume cavities 94 and 96 within the bore 50. The cavity 94 is a firstor drive cavity, the volume of which increases by virtue of the movementof the face defined by the step 90 in a direction away from the impactposition at the shank 14, while the second or upper cavity 96 decreasesin volume for movement in the same direction due to the movement of theface defined by the step 82. The upper cavity 96 is effectively sealedby the U-eup seals 98 around the section 78 of the piston 12. Theseseals 98 may be located in an upper part 99 of the sleeve 48; the part99 facilitating assembly of the piston in the housing 10. The lower ordrive cavity 94 is sealed by U-cup seals 100 disposed in the sleeve 48,around the lower section 84 of the piston 12. The sleeve 48 and theouter member 40 of the housing also form a third cavity 106 which is inthe form of a cylindrical gallery encompassing the bore 50 and laterallydisplaced therefrom.

The valve mechanism 85 is associated with the drive cavity 94. Supplyand return or discharge ports 102 and 104 respectively, are provided byperipheral internal grooves 105 and 107 in the sleeve 48. These groovesare in communication with the galleries 106 and 108 through lateralpassages 109 which occupy a substantial portion of the periphery of thesleeve 48 (see FIG. 38) to present a low inertance to the flow throughthe ports 102 and 104. The gallery [06 extends between the supply port102 and an opening 110 to the upper cavity 96 and thus communicates theupper cavity 96 and the drive cavity 94 when the supply port 102 isopen. The holes 76 in the inner part 60 of the supply accumulator 54also provide an essentially unrestricted channel which communicatesdirectly with the gallery 106 and therefore via the gallery with theupper cavity 96 and drive cavity 94. The supply accumulator holes 76 aredisposed opposite to an opening 112 in the housing section 40 which isdirectly adjacent the opening 110 and extends between these holes andthe gallery 106. A channel 114 connects the opening 112 to a coupling116 through which the supply line from a source of pressurized hydraulicfluid, say a hydraulic pump which supplies fluid pressures in the rangeof 2000 to 3000 psi. may be connected.

The return accumulator 56 also has the holes 76 which provide the entrychannel, in the front wall of its inner part 60 in direct communicationwith the lower gallery 108 such that the accumulator 56 is connected tothe drive cavity 94 when the return port 104 is open. The return linefor the hydraulic pump is connected to a coupling 118 to which a returnline 120 extends downwardly into the gallery 108 (see FIG. 2), thereturn line 120 being disposed behind the supply line 114.

Returning to the valve mechanism, in addition to the ports 102 and 104,the valve mechanism includes a valve element 122 in the form of a hollowcylindrical member or sleeve which is coaxial to lower section 84 of thepiston which is located between the rings 86 and 88 and which isslidably mounted with respect to the bore 50. The valve element is shownhaving longitudi nal dimension essentially equal to the distance betweenthe outer edges 123 and 125 of the grooves providing the supply andreturn ports 102 and 104. The inner periphery of the valve element isalso formed with longitudinally extending slots I24, (cusp-shaped incrosssection as shown in FIG. 3) which provide an unrestricted passagefor the hydraulic fluid therethrough. The lower edge of the ring 86engages the upper end of the valve element 122 as the piston moves downso as to open the supply port 102 and close the return port 104. Thering 88 engages the lower end of the valve element 122 as the pistonmoves up so as to open the return port 104 and close the supply port102. The upper and lower ends of the valve element are preferablyprovided with damping means such as steps which effectively form dashpots with the rings as more fully described in the above referencedBouyoucos application Ser. No. 285,240.

The large diameter (equal to the maximum piston diameter) of the valveelement 122 and its coaxial arrangement with respect to the large areagalleries 106 and 108 reduces inertance in the dynamic flow path andincreases power (I) nversion efficiency. This feature is especiallyadvantageous at high output power levels (i.e., high flows) whereinertance becomes even more significant. The large diameter valveenables the pressure drop across the ports to be maintained at a lowvalue until the last instant of valve closure, thereby reducinghydraulic power losses and providing high efficiency.

The operation of the impact tool as shown in FIGS 1, 2 and 3, will bemore apparent from FIGS. 4 through 7 which illustrate the piston 12 indifferent positions during its cycle of oscillation and from curves (0)through (d) in FIG. 9. FIG. 4 shows the piston 12 at the beginning ofthe cycle of oscillation with the piston in its displaced position atimpact with the shank [4. This is indicated as time I T The upper ring86 has moved the valve element I22 so that both the supply port 102 andthe return port 104 are momentarily closed. After the piston reaches theimpact position, the valve element may move, due to its own inertia. toa position below that shown in FIG. 4 where the supply port is open andthe return port closedv Pressurized fluid is supplied to the drivecavity 94 and accelerating forces are applied to the drive face formedby the step 90. The pressurized fluid is also applied to the uppercavity 96. The piston 12 has its differential area A,- presented to thepressurized fluid in these cavities 94 and 96; the area of the faceformed by the step being larger than the area of the face formed by thestep 82. The net force applied to the differential area is therefore inthe upward direction and accelerates the piston upwardly. The supplyaccumulator 54 tends to keep the pressure in the drive cavity 94constant since the compressed gas in the region 72 thereof acts as apressure release. The piston 12 then moves upwardly a distance X equalto the difference between the distance between the opposing faces of therings 86 and 88 and the length of the valve element 122. Theaccelerating forces are applied until the lower ring 88 moves the valveelement 122 to the position shown in FIG. 5, immediately after which thevalve element closes the supply port I02 and opens the return port 104.This occurs at a time in the cycle 1",. The pressure in the drive cavity94 is then switched from supply to return and the direction of force onthe piston is switched to decelerate the piston motion as shown in FIG.6. Energy has been transferred during the period from T to T to thepiston mass to give the piston kinetic energy.

After the piston 12 has travelled over a time period I T- T,, the pistonhas decelerated to zero velocity and has transferred its kinetic energyto the spring system presented by the hydraulic fluid in the cavity 96as well as in gallery 106 and in the supply accumulator 54. Inasmuch asthe accumulator 54 includes the pressure release region 72 which affordsa constant spring force (viz., the dynamic spring rate or stiffnessbeing reduced toward zero) a relaxation oscillator characteristic isobtained as shown in waveform (u) of FIG. 9 and in the waveforms at thetops of FIGS. 4 through 7. The energy introduced by the acceleratingforces applied to the piston during the time period T to T as well asits displacement over that interval, is then transferred back to thepiston to drive it downwardly towards impact. As shown in FIG. 7, duringthe time period I greater than T but less than T, T, being the impacttime at the end of the cycle, the discharge port 104 remains open whilethe supply port I02 remains closed. Port switching occurs immediatelyafter impact, and the impact reaction force assists the supply pressurein driving the piston upwardly to begin the next cycle of oscillation.The force on the average which is in the upward direction due to theimpact event and also in the upward direction during the time interval Tis balanced by forces in the downward direction during the time intervalfrom T to T The ratio of the areas presented by the steps 90 and 82 maynominally be 2:l, but may also be adjusted to provide a specific forcebalanced condition on average. The forces due to the impact events aswell as the losses in the system are considered in providing the exactratio.

The blow energy E applied to the shank 14 at the end of each cycle isproportional to the potential energy possessed by the piston at the topof its stroke at time I T This energy may be expressed by the followingequationz ll l s F I') (I) where k, is a constant, P is the supplypressure and )2 is the total piston travel to the top of its trajectory.In the case where the area of the step 90 is twice the area of the step82, the total piston travel distance to the top of its trajectory isapproximately twice the distance travelled over the time interval T toT,. The total piston travel is then given by:

The frequencyufm of oscillation may be derived from the kinetic andpotential energy relationships and may be expressed as where k is aconstant and M P is the mass of the piston.

The arrangement of the supply port 102, the opening 110 and the gallery106 provides a direct path and permits the fluid to flow back and forth(viz. exchange) between the upper cavity 96 and the drive cavity 94, soas with the aid of the supply accumulator 54, to provide the dynamicflow requirements of the tool and to reduce pressure fluctuations in thesupply region which might otherwise interfere with the oscillationcycle, Curve (1)) of HG. 9 shows the volume V,-,, transferred to thedrive cavity 94 through the supply port 102. This volume transfer occursduring the time interval T to T, and is equal to X,,A,, over theinterval T to T A,, is the area presented by the step 90 to the drivecavity 94. A,; is the area presented by the step 82 to the upper cavity96. Volume changes due to the compressibility of the hydraulic fluid andthe elasticity of the sleeve 48 and other housing members is neglectedfor purposes of explanation. Since the total piston travel in the upwarddirection is X, which is twice X for this exemplary case, the followingrelationships respecting the volume displacement V,, in the drive cavity94 and the volume displacement V in the upper cavity 96 exist.

The net volume supply to both the drive cavity and the upper cavity overthe time interval T to T during which interval the port to the drivecavity is open is therefore Hm N I-' 1,] 'tt' 'r' iil 4 1 As shown inequation (7) the net input volume displacement over the time intervalT,T is half the volume supplied to the drive area A (via, to the drivecavity 94) alone. Thus, the joining of the drive cavity and upper cavitythrough the gallery, during the time interval T,T creates less of aninstantaneous demand on the supply than would the requirements of thedrive cavity alone, and reduces the flow requirement from theaccumulator 54. Thus, the accumulator is better able to maintain thesupply pressure constant over the entire cycle of oscillation. Duringthe time interval from T to T,- the supply port 102 is closed so thatthe volume handled by the supply accumulator 54 is the differencebetween the input volume passing through the channel 114 and the volumedisplaced by the area A of the step 82. Over the first portion of thisinterval (between T, and T the area A is expelling fluid from the uppercavity 96 back into the supply accumulator 54. As the piston moves downthrough its full stroke, during the interval from T to Tp, the uppercavity 96 accepts flow from the accumulator 54 and from the supply in anamount equal to X A which amount is one-half the volume displaced fromthe drive cavity into the return accumulator 56.

In FIG. 9, the dashed lines represent the average dis placement rate.This is also the case in FIG. 10. The displacement curves of FIG. 9 (c)illustrate that when the common channel (gallery 106) interconnects theaccumulator 54 and the drive and upper cavities, the fluctuation orripple in the flow is reduced over the ripple which would exist if theupper cavity 96 was fed from a separate accumulator which would thenhave to supply the displacement shown in curve (b).

Curve (d) of FIG. 9 shows the volume displacement as seen by thedischarge accumulator 56. Over the time interval T., to T, the dischargeor return port I04 is closed, such that the volume does not change.Immediately after time T the port 104 opens, and the piston I2 iscontinuing its upward trajectory. Flow is therefore backwards throughthe port 104 and into the drive cavity 94. This flow is supplied by thedischarge accumulator 56. From time T to impact at time T,. the flow isout of the port 104 and the accumulator accepts a peak volumedisplacement X A The ripple or fluctuation as seen by the dischargeaccumulator 56 is greater than the ripple or fluctuations as seen by thesupply accumulator and shown in curve (c) of FIG. 9. However, suchfluctuations are at the low pressure of the discharge or return side ofthe tool which can be readily handled by the discharge accumulator. Ifit is desired to minimize such fluctuation and ripple, an impact tool inaccordance with the embodiment of the invention illustrated in FIG. 11or FIG. 13 may be used. The tool shown in FIG. 8 also minimizesfluctuations or ripple in the discharge accumulator. As will beexplained more fully hereinafter the fluctuations or ripple in the flowout of the discharge accumulator through the return channel may bereduced to that shown in curve (e) of FIG. 9.

Referring more particularly to FIG. 8, there is shown another impacttool having a housing 300. A sleeve 302 in the housing 300 together withinsert sleeves 304 and 306, which are provided for ease of assembly,define a bore 308 in which a piston 310 may oscillate in a directionalong the axis of the bore. A shank 312, for which a rotation mechanism.similar to that shown in FIG. I, may be provided, presents an impactsurface 314 for the lower end 316 of the piston 310. The piston 3I0 thusacts as a hammer for providing percussive forces upon impact with theshank 312. The shank may be connected to a drill steel and a bit fordrilling holes in a formation. say for construction, quarrying or miningpurposes.

The piston 310 has a central section 320 which is of greater diameterthan the diameter of the lower section 322 as well as the diameter of anupper section 324 of the piston 310. The lower section 322 has a largerdiameter than the upper section 324, such that opposite faces 326 and328 of the center section 320 respectively present a larger area and asmaller area to a first cavity 330 and a second cavity 332, the endboundaries of which are defined by the faces 326 and 328. While thesefaces 326 and 328 are shown in the form of steps, other boundarysurfaces of other shape may be provided, the term face being used todefine any such boundary surface in general. The first cavity 330provides a drive cavity for the piston and includes the valve mechanismfor switching the fluid pressure from supply to return therein, whilethe second cavity 332 is exposed to the supply pressure at all times.

A valve mechanism 334, consisting of a supply port 336, a return port338, a valve element 340, and spaced rings 342 and 344 on the piston 310which engage the valve element 340, is located in drive cavity 330. Theports 336 and 338 are provided by peripheral grooves which extendcircumferentially around the inner wall of the bore 308 as in a mannersimilar to that shown in FIG. 3B The opposite edges of the valve element340 provide porting edges which afford full peripheral porting to whichefficiency advantages mentioned above are attendant. The valve elementis slidably mounted within the bore 308 coaxial to the piston 310 andhas channels 346 which extend longitudinally thereof as was described inconnection with the valve element 122 (FIG. I).

The second cavity as well as the supply port 336 are in communication byway of lateral channels 348 and 350 with a circumferential gallery 352which extends therebetween. This gallery 352 is also in communicationwith a supply accumulator 354 by way of a large lateral opening 356 anda multiplicity of channels 358 in the wall of the accumulator 354 whichis adjacent to the opening 356. The accumulator 354 may be of a designsimilar to the accumulator 54 (FIG. I).

Another gallery encompasses the upper end of the drive cavity 330 and isin communication with the return port 338 via a lateral channel 362. Thegallery 360 is connected by way ofa large opening 364 to a returnaccumulator 366. A multiplicity of channels 368 in the wall of theaccumulator 366 adjacent the opening 364 provides direct communicationbetween the return accumulator 366 and the gallery 360. The returnaccumulator 366 may be similar to the return accumulator 56 (FIG. I Thereturn of the supply of pressurized hydraulic fluid is connected by wayof a channel 370 to the return gallery 360. A similar channel 37I intothe lateral opening 356 provides for connection of the supply for thesource of pressurized fluid to the supply gallery 352.

U-cups and O-ring seals, respectively for sliding sur faces andstationary surfaces are shown to seal the cavities and fluid channels inthe housing. Cleansing fluid, such as compressed air. may becommunicated through the piston 310 and the shank 312 by way of a pipe372 which extends through bores therein. as was described in connectionwith FIG. I.

The description of operation of the impact tool shown in FIG. 8, will beaided by reference being also made to FIG. 10. FIG. 8 depicts theposition of the piston 310 and the valve element 340 just at the instantof impact with the shank (viz, when the piston reaches the impactposition). The length of the valve 340 with respect to the return andsupply ports 338 and 336, and the position of the ring 342 on piston 310is such that the return port 338 will immediately become opened and thesupply port 336 closed as the valve element 340 travels downwardsomewhat from the position shown in FIG. 8. Then, during the firstportion of the cycle of oscillation, from T, to T (see FIG. 10 (a)),pressurized fluid is applied to the second cavity 332 but the drivecavity 330 is open to return by the valve mechanism. The ratio of theareas of the faces 326 to 328 is preferably of the order of 2:l. Thepressurized fluid acting on the face 328 drives the piston upwardly in adirection away from the impact position.

When the lower ring 344 on piston 3I0 raises the valve element 340 tothe position shown in FIG. 8, switching occurs in the drive cavity.Pressurized fluid is then applied by way of the gallery 352 to both thesecond and drive cavities. The net force on the piston 310 has nowreversed and is in a direction toward the shank. The return port 338 isclosed. The initial momentum of the piston 3I0 enables it to be carriedupward to the limit of its displacement X (See FIG. 10 (u)). Net flow isinto the accumulator 354. At the top of its stroke at time T the kineticenergy of the piston is stored in the accumulator 354 as well as in thefluid in the cavities and galleries and channels associated therewith.The piston 310 is then driven downwardly during the period T, to T,. andover the entire displacement X, to the impact position. Then the valvemechanism is activated and the return port 338 is opened and the supplyport 336 is closed causing the cycle to repeat. The energy stored in theaccumulator is transferred during the period T to T,- into percussiveforces which are transmitted to the shank 312 and via the shank to thedrill steel and bit for rock drilling or other purposes.

The characteristics of the massive piston. the springlike fluid in thecavities. galleries and channels as well as the accumulator. define arelaxation oscillator which develops percussive forces especiallyadapted for timedependent loads such as are encountered in rockdrilling.

As shown in FIG. (b). the flow into the drive cavity 330 is cut offduring the initial portion of the cycle from 'I], to T,. Then flowduring the second part of the cycle from T, to T is outward from thedrive cavity as the kinetic energy of the hammer is stored in the fluid,springs. and accumulator 354. The displacement of fluid into the secondcavity 332 increases from T. to T and then decreases (outward from thecavity) during the remainder of the cycle from T to T,.. The flow fromthe second cavity is communicated with the gallery 352 and. whencombined with the flow to the first cavity. tends to reduce the netdynamic flow requirements from the accumulator. The net dynamic flowfrom the accumulator 354 is illustrated in curve (1') of FIG. 10. Itwill be seen from this curve that the net flow fluctuations are reducedfrom those associated with the first or drive cavity.

The flow fluctuations to the return accumulator 366 as seen by thereturn channel 370 exists only during the first portion ofthe cycle fromT., to T as shown in FIG. 10 ((1) since thereafter the return port isclosed. It will be seen. therefore. that the fluctuations in the returnpath of the configuration of FIG. 8 are generally re duced relative tothose present in the configuration of FIG. I. In particular, thedischarge fluctuations of FIG. I0 ((1) compared with those of FIG. 9(d). are seen to be only half as large.

As will be seen. reduced discharge fluctuations can also be provided forin the configuration of FIG. I by means of an auxiliary return cavityillustrated as cavity 170 (FIG. II) and discussed in connection withFIG. 9 (0).

Referring to FIG. ll. there is shown an impact tool having a hammer 130movable in a bore within a hous ing 132. The housing has also mountedthereon a sup ply accumulator I40 and a return accumulator 142. Thesupply line 144 from the source of pressurized hydraulic fluid (eg. ahydraulic pump) enters into the supply accumulator 140. A return lineI46 enters the return or discharge accumulator 142.

A small diameter step 148 and a large diameter step I50 on the piston130, which provide faces forming the differential area, also partiallybound the second cavity 152 and the first cavity I54, respectively, inthe hous ing 132. A gallery 156 communicates the second and firstcavities I52 and 154 when the supply port I58 is opened by the valveelement 160. The valve element I60 also switches the fluid pressure inthe first cavity I54 from supply pressure to return pressure by closingthe supply port 158 and opening the return port I62. The impact tool asshown in FIG. 11 thus operates like (ill the tool shown in FIG. 1. andthe supply pressure fluctuation is minimized by virtue of theinterconnection of the first and second cavities, as was explained inconnection with FIGS. 1 through 8.

In o der to minimize the fluctuations in the discharge flow. the impacttool shown in FIG. 1] is equipped with a lower piston section 164, whichwith the piston section I66 adjacent thereto forms a step 168. Thepiston section 164 has the same area as the section of the pistonproviding the step I50. This step 168 bounds one end of a lower cavity170 which varies in volume. as the piston [30 moves. in a sense oppositeto the variation in volume ofthe first cavity 154. Accordingly. thepressurized fluid can flow back and forth between the first cavity andthe cavity 170 by way of a gallery 174 which provides communicationtherebetween. The discharge accumulator also opens into the gallery 174by way of an unrestricted passage 176.

When the discharge port 162 is open the volume flow through thedischarge port caused by the motion of the face presented by the stepISO is equal. but opposite in sign, to the volume flow due to the pistonstep 168. The discharge accumulator [42 therefore does not see any netvolume displacement. It is only when the discharge port 162 is closedthat the discharge accumulator sees a volume displacement. This isduring the interval T to T when the piston is being accelerated in theupward direction away from the impact load. During the interval T to Tvolume displacement into the discharge accumulator 142 is. provided bythe lower cavity due to the movement ofthe step 168. This volumedisplacement in the discharge accumulator as seen by the return channelI46 is shown in curve (4.) of FIG. 9. The discharge pulsation is thusreduced to approximately one-half the fluctuation shown in curve ((1) ofFIG. 9 which depicts the case illustrated in FIG. I where a lower cavityis not used.

Referring to FIG. I2, a housing is provided with a bore 182 in which thehammer of the tool. provided by a piston 184, oscillates. A supplyaccumulator I86 and a return accumulator 188 are shown located onopposite sides of the housing 180. While such location provides a morebalanced size and weight relation which may be desired in someapplications for impact tools. other accumulator locations may be used.The tool has a first cavity 190 and a second cavity 192. The firstcavity performs the same function as the first cavity 94 of FIG. I whilethe second cavity 192 performs the same function as the cavity 96 ofFIG. I. however their positions are reversed. Such reversal provides thefeature of simplification of the construction of the piston 184. Thepiston may be a two-part structure con sisting of a lower part I94, theupper end of which I96 is threaded. The upper part 198 of the piston isin the form of an internally threaded disc having an axially extendingrim 200. The entire part 198 may be screwed onto the threaded end 196 ina manner of a nut. A

valve element 202, can. by virtue of the two-part construction of thepiston 184. be assembled on the piston in the first cavity 190. The sametwo-part construction feature can be implemented in connection with theconfiguration shown in the other FIGS. of the drawing, including FIGS. 1and 8.

The valve element 202 in FIG. 12 is provided with a centrally disposedlip 204 which is engaged between the rim 200 and a shoulder 206 of thepiston I84. The rim 200 and shoulder 206 are spaced longitudinally fromeach other a distance relative to the length of the lip 204 of the valve202 to provide the desired delay displacement and free stroke X of thevalve 202. The valve element 202 is also vented by way of holes 208which extend longitudinally therethrough. A number of such holes, whichperform the same function as the groove 90 in the valve element 122(FIG. 1) are distributed around the valve element 202.

The second cavity 192 is connected to the first cavity 190 by way of achannel 210. The supply line 212 also communicates with the channel 210.The supply accumulator 186 opens into the channel 210 through a port214. Accordingly, when the supply port 216 is open, volume flow from thesecond cavity 192 to the first cavity 190 partly compensates for thefirst cavity requirements, thereby minimizing the total volumedisplacement required from the supply accumulator 186. The accumulator186 provides flow to the second cavity 192 when the return or dischargeport 218 is opened and the supply port 216 is closed. Accordingly, thefluctuations are minimized and maintenance of constant prcssure aided aswas explained in connection with FIG. 1. The discharge port 218 isconnected to the discharge accumulator 188 via an opening 219. Thereturn line 220 also enters into this opening. The dischargefluctuations are similar to those depicted in FIG. 9 (d).

The impact tool shown in FIG. 13 is similar to the tool shown in FIG.12, like parts being identified with like reference numerals. Anadditional cavity 230 is partially bounded by a piston step 232 of thesame area as the piston step 234 which defines and varies the volume ofthe first cavity 190. The step 234 has a larger area than the step 236which defines and varies the volume of the second cavity 192.

To provide for the volume flow back and forth between the additionalcavity 230 and the drive cavity 190, a channel 240 is provided whichextends longitudinally between the discharge port 218 and the additionalcavity 230. The return accumulator also is connected to the channel 240by way of an opening 242. The return line 220 also enters the channel.It will therefore be observed that the flow fluctuations in the impacttool shown in P16. 13 are minimized, both as regards the supply and thereturn flows.

Referring to FIG. 14, there is shown an impact tool which is similar,insofar as the construction of its piston 184 is concerned, with thetool shown in FIG. 12 and like parts of these tools identified with likereferenced numerals. The valve element 202 is provided with a pcripheralslot 250 which is centrally located between the upper and lower ends ofthe valve element 202. The slot communicates with the vents 208. Theporting between the supply and return ports 216 and 218 is thereforethrough the slot 250. The effective length of the valve ele ment 208 istherefore the width (in the vertical direction) of the slot 250.

The supply port 216 is now located below the return port 218. Thispermits the channel 210 (FIG. 12) to be provided by a gallery 252 whichextends circumferentially around the housing and encircles the piston184. The use of this gallery simplifies the construction of the housingand assures unrestricted communication between the first cavity 190 andthe second cavity 192.

From the foregoing description it will be apparent that there has beenprovided improved impact tools which generate percussive energy. Whilevarious embodiments of the tools which incorporate the invention havebeen described for purposes of illustration, variations andmodifications therein the scope of the invention will undoubtedlysuggest themselves to those skilled in the art. Accordingly, theforegoing description should be taken as illustrative and not in anylimiting sense.

What is claimed is:

1. An impact tool for generating percussive forces, said toolcomprising:

a housing have a bore,

a piston disposed for oscillatory movement in said bore over a forwardstroke toward and over a return stroke away from an impact positionduring each cycle of oscillation of said piston,

said piston having faces which define the end bound aries of first andsecond variable column cavities in said bore, the volumes of which varyin opposite senses when said piston moves in said bore,

the area of the one of said faces which defines said first cavity beinggreater than the area of the other of said faces which defines saidsecond cavity.

means in said housing whereby pressurized fluid is supplied thereto andreturned therefrom,

a valve mechanism associated with said first cavity having ports in saidfirst cavity spaced from each other axially with respect to said boreand respectively in communication with said supply and said return ofsaid last-named means, a valve element in said first cavity extendingaxially between said ports and movable with said piston for closing saidsupply port and opening said return port after displacement of saidpiston over a first predetermined distance in one direction during saidforward stroke and for opening said supply port and closing said returnport after displacement of said piston over a second predetermineddistance in the opposite direction during said return stroke, saidsecond predetermined displacement being substantially less than saidreturn stroke whereby said return port is open for a shorter period oftime than said supply port is open during each said cycle, and

means in said housing providing communication between said supply andsaid second cavity for apply ing forces to said other piston face todrive it in a direction away from said impact position when said valveelement opens said return port and closes said supply port.

2. The invention as set forth in claim 1 wherein said piston has asection of cross-sectional shape and size substantially equal to thecross-sectional shape and size of said bore, said faces being oppositeends of said piston section, said other of said faces being closer tosaid impact position than said one face.

3. The invention as set forth in claim 2 further comprising a shank insaid bore presenting an impace surface to one end of said piston.

4. The invention as set forth in claim 1 wherein said valve element is atubular member coaxial with said bore and encompassing said piston andis slidable along said bore across said ports, projections extendingfrom one of said tubular member and said piston for directly engagingapplying force to said tubular member for moving said tubular member.

5. The invention as set forth in claim 4 wherein said cavities aregenerally cylindrical chambers provided in said housing, and said portsare separate peripheral grooves in said chamber for said first cavitywhich are opened and closed by porting edges of said tubular member.

6. The invention as set forth in claim I including energy storage meansassociated with said second cavity and with said first cavity when saidsupply port is open.

7. The invention as set forth in claim 6 wherein said energy storagemeans is an accumulator.

8. The invention as set forth in claim 7 wherein said fluid is ahydraulic fluid and said accumulator has a fluid filled region and anadjoining region filled with a confined gas. said regions beingseparated by a yieldable member, said fluid filled region being incommunication with said second cavity and said first cavity when saidsupply port is open.

9. The invention as set forth in claim 7 including a second accumulatorassociated with said first cavity when said return port is open. andpassage means in said housing presenting low inertance to the flow ofsaid fluid between said second accumulator and said first cavity whensaid valve element closes said supply port and opens said return port.

10. The invention as set forth in claim 6 including a gallery in saidhousing encompassing said bore and spaced outwardly therefrom, saidgallery extending between said supply port and said second cavity andbeing in communication therewith and with an accumulator which providessaid energy storage means.

ll. An impact tool for applying percussive forces to a load. said toolcomprising a housing having a bore therein.

a piston mounted in said bore for oscillatory movement axially of saidbore in a first direction toward said load and in a second directionaway from said load. said piston having a section having first andsecond faces at opposite ends of said section, said first face facingaway from said load and defining the end boundary of a first cavity insaid bore, said second face facing toward said load and defining the endboundary of a second cavity in said bore. the volumes of said cavitieschanging in opposite sense with movement of said piston in either ofsaid directions, said first face being larger in area than said secondface,

pressurized hydraulic fluid supply and return passages in said housing.said second cavity being in communication with the supply passage forfilling said second cavity with pressurized fluid which ex erts force onsaid second face in the direction away from said load,

a valve mechanism in said first cavity including a sleeve slidablymounted in said bore for movement axially thereof. means providing formoving said sleeve with said piston during final portions of itsdisplacement in said first direction and during final portions of itsdisplacement in said second direction for respectively communicatingsaid first cavity with said return passage for causing said forcesapplied to said second face to move said piston in the direction awayfrom said load and with said supply passage for applying forces to saidfirst face in the direction toward said load. said final portion of saiddisplacement in said second direction being a substantial portion ofsaid displacement in said second direction,

fluid energy storage means, and

means communicating said energy storage means with said second cavity.with said supply means and also with said first cavity, when said valvemechanism communicates said supply with said first cavity, and forstoring energy in said storage means when said piston is moving awayfrom said load. thereby to bring said piston movement to a stop. saidenergy being returned to said piston as said piston accelerates back inthe direction toward said load for applying said percussive forcesthereto. said communicating means also providing an unrestricted passagefor the exchange of fluid between said first and second cavities forreducing fluctuations in flow with respect to said storage means.

1. An impact tool for generating percussive forces, said toolcomprising: a housing have a bore, a piston disposed for oscillatorymovement in said bore over a forward stroke toward and over a returnstroke away from an impact position during each cycle of oscillation ofsaid piston, said piston having faces which define the end boundaries offirst and second variable column cavities in said bore, the volumes ofwhich vary in opposite senses when said piston moves in said bore, thearea of the one of said faces which defines said first cavity beinggreater than the area of the other of said faces which defines saidsecond cavity, means in said housing whereby pressurized fluid issupplied thereto and returned therefrom, a valve mechanism associatedwith said first cavity having ports in said first cavity spaced fromeach other axially with respect to said bore and respectively incommunication with said supply and said return of said last-named means,a valve element in said first cavity extending axially between saidports and movable with said piston for closing said supply port andopening said return port after displacement of said piston over a firstpredetermined distance in one direction during said forward stroke andfor opening said supply port and closing said return port afterdisplacement of said piston over a second predetermined distance in theopposite direction during said return stroke, said second predetermineddisplacement being substantially less than said return stroke wherebysaid return port is open for a shorter period of time than said supplyport is open during each said cycle, and means in said housing providingcommunication between said supply and said second cavity for applyingforces to said other piston face to drive it in a direction away fromsaid impact position when said valve element opens said return port andcloses said supply port.
 2. The invention as set forth in claim 1wherein said piston has a section of cross-sectional shape and sizesubstantially equal to the cross-sectional shape and size of said bore,said faces being opposite ends of said piston section, said other ofsaid faces being closer to said impact position than said one face. 3.The invention as set forth in claim 2 further comprising a shank in saidbore presenting an impace surface to one end of said piston.
 4. Theinvention as set forth in claim 1 wherein said valve element is atubular member coaxial with said bore and encompassing said piston andis slidable along said bore across said ports, projections extendingfrom one of said tubular member and said piston for directly engagingapplying force to said tubular member for moving said tubular member. 5.The invention as set forth in claim 4 wherein said cavities aregenerally cylindrical chambers provided in said housing, and said portsare separate peripheral grooves in said chamber for said first cavitywhich are opened and closed by porting edges of said tubular member. 6.The invention as set forth in claim 1 including energy storage meansassociated with said second cavity and with said first cavity when saidsupply port is open.
 7. The invention as set forth in claim 6 whereinsaid energy storage means is an accumulator.
 8. The invention as setforth in claim 7 wherein said fluid is a hydraulic fluid and saidaccumulator has a fluid filled region and an adjoining region filledwith a confined gas, said regions being separated by a yieldable member,said fluid filled region being in communication with said second cavityand said first cavity when saId supply port is open.
 9. The invention asset forth in claim 7 including a second accumulator associated with saidfirst cavity when said return port is open, and passage means in saidhousing presenting low inertance to the flow of said fluid between saidsecond accumulator and said first cavity when said valve element closessaid supply port and opens said return port.
 10. The invention as setforth in claim 6 including a gallery in said housing encompassing saidbore and spaced outwardly therefrom, said gallery extending between saidsupply port and said second cavity and being in communication therewithand with an accumulator which provides said energy storage means.
 11. Animpact tool for applying percussive forces to a load, said toolcomprising a housing having a bore therein, a piston mounted in saidbore for oscillatory movement axially of said bore in a first directiontoward said load and in a second direction away from said load, saidpiston having a section having first and second faces at opposite endsof said section, said first face facing away from said load and definingthe end boundary of a first cavity in said bore, said second face facingtoward said load and defining the end boundary of a second cavity insaid bore, the volumes of said cavities changing in opposite sense withmovement of said piston in either of said directions, said first facebeing larger in area than said second face, pressurized hydraulic fluidsupply and return passages in said housing, said second cavity being incommunication with the supply passage for filling said second cavitywith pressurized fluid which exerts force on said second face in thedirection away from said load, a valve mechanism in said first cavityincluding a sleeve slidably mounted in said bore for movement axiallythereof, means providing for moving said sleeve with said piston duringfinal portions of its displacement in said first direction and duringfinal portions of its displacement in said second direction forrespectively communicating said first cavity with said return passagefor causing said forces applied to said second face to move said pistonin the direction away from said load and with said supply passage forapplying forces to said first face in the direction toward said load,said final portion of said displacement in said second direction being asubstantial portion of said displacement in said second direction, fluidenergy storage means, and means communicating said energy storage meanswith said second cavity, with said supply means and also with said firstcavity, when said valve mechanism communicates said supply with saidfirst cavity, and for storing energy in said storage means when saidpiston is moving away from said load, thereby to bring said pistonmovement to a stop, said energy being returned to said piston as saidpiston accelerates back in the direction toward said load for applyingsaid percussive forces thereto, said communicating means also providingan unrestricted passage for the exchange of fluid between said first andsecond cavities for reducing fluctuations in flow with respect to saidstorage means.